I don't know if it's a good sign. Like, their enforcement is good enough to root out these top performers.

Or if it's a bad sign. Like, everyone is doping and only a couple get caught.

It is interesting though, that even in these "busts" they aren't really getting caught doping. Coleman is banned for whereabouts violations (missing surprise testing). There are others I know of that got caught up with this.
Rollins is banned for some sort of tampering.
It's been a while since I've been aware of a straight up positive test, particularly in the US